One solution to the problem of sensory neural (inner ear) deafness is to bypass the damaged hair cells of the inner ear and directly stimulate the remaining auditory nerve fibers electrically. A major obstacle to this proposed treatment has been the lack of an implantable electrode system which will: (1) provide the necessary frequency specificity (by stimulating small discreet groups of auditory nerve fibers according to their normal frequency arrangement within the inner ear); (2) be small and flexible enough to be inserted the required distance into the inner ear without damaging the remaining auditory nerve fibers; and (3) contain the number of channels (approximately 15) necessary for speech discrimination without either shorting or breaking the conductors during insertion. Through the combined efforts of an Otologic Surgeon - Physiologist and an Electrical Engineer specializing in printed circuit development, we have undertaken the task of developing such an "implant". The prototype of this device consists of two multi-channel printed circuit teflon ribbons sandwiched in a silicone rubber carrier and will be inserted into the squirrel monkey's inner ear using current surgical techniques. The intent of this project is to determine the stimulating electrode surface area, spacing between the electrodes, and electrical stimulus parameters which will produce resposes in the auditory nerve fibers which are closest to those produced by normal hearing and will, therefore, have the greatest potential for producing intelligible speech. We will also determine the electrical interaction between adjacent electrode channels so that unwanted interaction may be avoided. The prototype electrode developed in this project will eventually lead to the cochlear implant used in the treatment of inner ear deafness in humans after further animal testing has proven its long-term safety.